A 68-year-old woman is brought to an urgent care center by her family due to a rapid onset of confusion, agitation, and unusual movements over the past 24 hours. Her family reports she has a history of major depressive disorder, essential hypertension, and Parkinson's disease. Her current medications include escitalopram, perindopril, and rasagiline, which was recently initiated a week ago for her worsening Parkinsonian symptoms. She also takes over-the-counter dextromethorphan for a persistent cough. On examination, she is disoriented to time and place, markedly agitated, and diaphoretic. Her temperature is 38.8 °C, blood pressure is 145/95 mmHg, pulse is 125 beats/min, respiratory rate is 24 breaths/min, and oxygen saturation is 98% on room air. Neurological assessment reveals generalized hyperreflexia, particularly prominent in the lower extremities, and spontaneous ankle clonus. She also exhibits diffuse muscular rigidity. Laboratory results are pending but preliminary bedside glucose is 6.5 mmol/L. Based on her presentation, what is the most likely diagnosis and the immediate therapeutic intervention required?